Our research objectives will be focussed on the following problems: 1. The mode of operation of Na-K cotransport. We will test the hypothesis that Na-K cotransport operates to accumulate K but not to extrude Na ions against its electrochemical gradient. 2. Kinetics of the Na-Na exchange system. We will investigate the affinity for internal Na of the Na-Na exchange system blocking Na-K cotransport. The effect of changes in membrane potential, intracellular calcium, and cyclic-AMP levels will be investigated. The affinity for internal Na of the Na-Na exchange system will be investigated in red cells of normotensive and hypertensive patients.